The present invention relates to a pressure sensor, a method for manufacturing a pressure sensor, and an internal combustion engine having a pressure sensor.
Pressure sensors are used in various branches of engineering in order to measure the pressures of gases or liquids. The pressure sensors are often subjected to high loads that depend on the current state of the medium in which the measurement is performed. Frequently, the pressures acting on the pressure sensor vary considerably. A pressure sensor must therefore withstand high loads, and it must deliver exact measuring results.
Conventional pressure sensors include a diaphragm, which deforms in response to a pressure difference on the two sides of the diaphragm. The deformation of the diaphragm is measured by piezoelectric elements, which are situated on one side of the diaphragm.
In the case of high pressure or temperature loads, there is the problem of the pressure-sensor diaphragm twisting or warping in its frame or suspension. The consequences include inaccurate measurements or invalid measuring results, which occur in response to high pressure or temperature fluctuations.
Therefore, it is an object of the present invention to provide a pressure sensor, which delivers accurate measuring results, and may be configured so that it withstands high pressures, and functions reliably in the case of large pressure or temperature differences. It is another object of the present invention to provide a method for manufacturing such a pressure sensor which may be implemented quickly and cost-effectively. It is a further object of the present invention to provide a combustion engine that may attain lower emissions and/or an improved efficiency.
The above and other beneficial objects of the present invention are achieved by providing a pressure sensor, a method for manufacturing a pressure sensor and a combustion engine as described herein.
The pressure sensor according to the present invention includes a housing, the interior chamber of which is sealed by a diaphragm, an arrangement configured to generate a signal in response to the diaphragm being deformed, and also a flexible measuring element, which is included in addition to, i.e., positioned separately from the diaphragm, and is coupled to the diaphragm. The arrangement configured to generate a signal being coupled to the flexible measuring element, in order to generate the measuring signal in response to the flexible measuring element deforming.
The pressure sensor according to the present invention prevents the measuring results from being invalidated by twisting or warping of the diaphragm. The additional, flexible measuring element positioned separately from the diaphragm allows measuring results to be achieved, which are still relatively accurate, even in the case of a diaphragm that is twisted or warped in itself. The pressure sensor may even perform accurate and reliable measurements in the case of high pressures or pressure differences, and/or in the case of sharply changing temperatures, the pressure sensor also having an increased service life.
The measuring element may include a bendable bar, one end of which is freely suspended. In this manner, a deformation of the diaphragm, which is caused by a pressure acting on the diaphragm, may be transmitted to the bendable bar, and the pressure may be picked up and measured separately from the deformation of the diaphragm. The measuring or deformation element may, for example, be formed in the shape of a tongue. The measuring signal is generated by the deformation of the measuring element. The bar may relax in response to undesired twisting or warping. This prevents the measuring results from being invalidated. In addition, the pressure sensor may include a stop element, which opposes the deformation force in response to a selected deformation of the measuring element. This arrangement provides overload protection against high pressures, the overload protection being independent of the output signal. That is, the measuring element may be designed for high sensitivity and nevertheless withstand relatively high pressures. Therefore, there is no loss of sensitivity at the measuring element, even in the case of high pressure loads. The pressure sensor may also measure the applied pressure under high pressure loads, without the danger of destroying the measuring element. The stop element may be rigid, so that the measuring element does not bend or deform further upon reaching the stop, or the stop element may be designed to be bendable or flexible.
The stop element may be in the form of a second, flexible measuring element, which, for example, is harder or flexurally stiffer than the first measuring element. This arrangement allows the pressure sensor to have a plurality of measuring ranges and to be, e.g., suitable for measuring in the low pressure range and also, or simultaneously, in the high pressure range. At relatively low pressures, only the first measuring element is initially deformed. The stop element or second, flexible measuring element also deforms at or beyond a selected deformation of the first measuring element.
Because of the high resistance of the stop element or second measuring element, the first measuring element only bends or deforms a little more, even at high, applied pressures, so that it is protected from overload. Thus, at or above a selected pressure, it is only possible to further deform the first and the stiffer, second measuring elements at relatively high pressures. Therefore, the second measuring element opens up an additional measuring range for relatively high pressures.
The stop element may be configured as a half-open or semienclosed diaphragm, or it may be tongue-like or a bendable bar, the end of which may be freely suspended. The stop element may be fixed on one end. The stop bar may be configured similarly to or exactly like the first measuring element.
The first measuring element and/or the second measuring element may be provided with one or more piezoelectric elements as the arrangement configured to generate signals. For example, the signal generation arrangement may include piezoresistors, which may be connected to a Wheatstone bridge.
The pressure sensor may include a deformable transmission element configured to transmit force between the diaphragm and the measuring element and/or the stop element. The transmission element may have a selected elasticity or bending resistance. For example, the measuring range or the measuring ranges of the pressure sensor are determined by the stiffness or hardness of the transmission element. In this manner, measurements may be performed at relatively high pressures applied to the diaphragm using a relatively soft measuring element having a high sensitivity.
The transmission element may be configured as a diaphragm and/or as a chip, and its thickness is selected for determining the measuring range or the measuring ranges of the pressure sensor. That is, the measuring range or the measuring ranges of the pressure sensor may be controlled by varying or selectively setting the thickness of the transmission element or the transmission diaphragm.
The transmission element may be configured to be stiffer than the diaphragm or steel diaphragm. Therefore, adjustment inaccuracies during assembly carry over correspondingly less sharply to the transmission element than to the diaphragm. The steel diaphragm or diaphragm deflects outwardly to a greater degree than the transmission element deflects inwardly.
The first measuring element and/or the second measuring element may be configured as a bar or tongue in a chip, the two measuring elements being disposed in a single chip, which consequently forms a measuring chip.
The pressure sensor may have at least two measuring ranges, e.g., the first measuring range covering a range of 0 to 20 bar, e.g., 0 to 10 bar or 0 to 2 bar, while, e.g., the second measuring range covers a range of 0 to 300 bar, e.g., 0 to 250 bar or 0 to 200 bar.
The pressure sensor may have overload protection, which, for example, may be in the range of 250 bar.
The deformable or flexible diaphragm may be manufactured from steel. This arrangement allows the diaphragm to be connected to the housing in a particularly effective and secure manner, e.g., by welding. In the case of using steel or metal as a material for the diaphragm and the housing, the thermal coefficients also match each other very well, so that the measurement accuracy and stability are also high in the case of variable temperatures or temperature fluctuations.
At least one of the elements of the pressure sensor, e.g., diaphragm, transmission element, measuring element, and/or stop element, may be manufactured with an aiming-off allowance in order to compensate for manufacturing tolerances during coupling, the diaphragm being lightly curved to the outside due to the aiming-off allowance.
Furthermore, the present invention provides a method for manufacturing the pressure sensor, the method include the steps of: providing a housing having an interior chamber, which is sealed or may be sealed by a diaphragm; providing a support structure, which, for example, supports at least one bendable or flexible measuring element on its upper side; inserting the support structure along with the bendable measuring element into the housing; and sealing the interior chamber. Using this method, a pressure sensor having a high measurement accuracy may be manufactured in a relatively simple and, therefore, inexpensive manner. The method may be used for manufacturing a pressure sensor as described above.
A stop element or a second bendable measuring element, which, in the installed state, opposes a deformation force at or above a predetermined pressure on the diaphragm, may be on the support structure or its upper side.
During manufacturing, manufacturing tolerances may be compensated for by an aiming-off allowance, and the diaphragm, for example, is slightly pressed to the outside by the transmission element or another component part. This allows a high degree of accuracy to be achieved over the entire measuring range, even when the component parts are not exact.
The support structure or base plate may be fixed in place, preferably by a sleeve or a ring, after, e.g., inserting, introducing or mounting the support structure. The diaphragm may be welded to the housing.
The pressure sensor according to the present invention may measure the applied pressure under high pressure loads with a high degree of accuracy. The pressure sensor may be designed to simultaneously measure high and low pressures, the pressure sensor also having a high resolution in the low pressure range. Measurements may be taken in the high and low pressure ranges without costly, additional arrangements, such as, e.g., various pieces of electronic amplifying equipment. The time and the costs are especially reduced, since it is not necessary to switch over between ranges. In addition, the pressure sensor only requires a small space.
An application may include in determining the combustion chamber pressure or cylinder pressure in an internal combustion engine, in order to improve combustion or achieve an improved efficiency in conjunction with a suitable control system. For example, the pressure is accurately measured during the intake or exhaust stroke, the pressure sensor simultaneously withstanding the high pressures occurring in the combustion chamber during the combustion process. In this context, any such engine, e.g., an Otto or diesel engine, may include such a pressure sensor. The pressure sensor may, for example, be arranged in the wall of an engine cylinder.